Heart rate variability monitoring involves monitoring the heart beat rate and discerning the rate at which the heart beat rate changes. This rate is generally referred to as “heart rate variability” or HRV. The HRV cycle may be used for diagnostic purposes by a health care professional and it may be fed back to the user for purposes of effecting a change in psychophysiological status. The HRV cycle may be monitored by any means that detects the pulse and measures the inter-beat interval, also know as the “rise-rise” interval. The HRV cycle is typically plotted and displayed graphically for purposes of diagnosis and or biofeedback. A patient or user is typically encouraged to work on modifying amplitude, the average difference between the peak and the valley of the HRV cycle, or the “coherence”, i.e. consistency of amplitude, phase, and frequency thereof, for remedial purposes.
It is generally assumed that the heart rate variability phenomenon is a result of autonomic nervous system regulation of blood pressure via the baroreceptor reflex. However, it has not been clear to what the baroreceptor is actually responding.
If this is so, then heart rate variability is a step removed from the actual phenomenon that produces it, i.e. changes in arterial pressure. The more effective and immediate means of moderating physiologic status would be to monitor and feed back the respiratory arterial pressure wave itself. However, until now, it has not been clear why or how the arterial pressure wave is created, or how to monitor it.
To this end, this invention specifies a method for detecting the respiratory arterial pressure wave as a function of blood volume, monitoring the dynamic respiratory arterial pressure wave, measuring its primary physical attributes, and presenting it for diagnostic and or remedial biofeedback purposes.
Under normal quiescent circumstances, arterial pressure is primarily a function of heart beat rate, heart output, and arterial capacity, these factors being regulated by the autonomic nervous system. However, respiration has a very strong effect, dynamic respiratory arterial pressure rising and falling with exhalation and inhalation respectively. This is due to the fact that during deep respiration the lungs and thoracic cavity act as a reservoir for blood, storing it before forwarding it to the left side of the heart and onto the systemic arterial tree.
The pulmonary arterial tree stores 450 ml of blood under normal breathing circumstances, where normal is defined as being relatively fast and shallow, for example 15 breaths per minute with commensurate depth. The pulmonary arterial tree is highly elastic and conforms to changes in thoracic pressure as a function of diaphragmatic action, inhalation or downward movement of the diaphragm resulting in negative thoracic pressure, and exhalation or upward diaphragmatic movement resulting in positive thoracic pressure. The extent of negative and positive pressure depends on the extent of inhalation and exhalation respectively, more complete inhalation and exhalation resulting in stronger negative and positive pressures, respectively. This alternating negative and positive pressure is the reason that air enters the lungs from the external environment coincident with inhalation and exits the lungs coincident with exhalation.
Because of its high elasticity, the pulmonary arterial tree is capable of accommodating up to twice as much blood or ˜950 ml during deep inhalation, and evacuating twice a much during deep exhalation. When a person inhales deeply the resulting negative thoracic pressure results in accelerated venous blood flow, filling expanding pulmonary arteries via the right side of the heart. This “storage” reduces blood exiting the lungs toward the left side of the heart, lowering total heart output and systemic arterial pressure. The autonomic nervous system responds to this change by increasing heartbeat rate and constricting (narrowing) arteries, increasing pressure in the arterial tree and thereby limiting the drop due to pulmonary blood storage.
Upon exhalation, the heretofore negative pressure becomes positive, pulmonary arteries contract under positive pressure, forwarding blood through the pulmonary veins to the left side of the heart and into the systemic arterial tree. This results in an increase in systemic arterial pressure. The autonomic nervous system responds to this change by reducing heart beat rate, yet increasing ejection fraction, and relaxing arteries, i.e. enlarging arterial capacity. The net effect is that pressure in the systemic arterial tree increases yet is maintained within viable limits. This results in the respiratory arterial pressure wave that washes through the systemic arterial tree coincident with exhalation.
Baroreceptors are specialized neurons located throughout the arterial system. Their function is that of monitoring arterial pressure. When the baroreceptors sense a decrease in pressure, the autonomic nervous system facilitates an increase. When they sense an increase, the autonomic nervous system facilitates a decrease. In this way, the baroreceptors, in combination with the autonomic nervous system, work in opposition to changes in dynamic respiratory arterial pressure.
The aforementioned relationship between arterial pressure and heart rate is in fact a primary impetus for the heart rate variability phenomenon. Consequently, by monitoring the heart rate variability cycle, at rest, we are able to discern, amongst other things, changes in arterial pressure, rising heart beat rate being indicative of decreasing arterial pressure and falling heart rate being indicative of increasing pressure, heart rate having an inverse relationship with arterial pressure.
This invention proposes the fundamental method of monitoring and utilizing the dynamic respiratory arterial pressure wave itself as the basis for diagnosis and biofeedback for purposes of assessing health condition and or evoking a physiologic change. The advantage of this is that the dynamic respiratory arterial pressure wave is the first order physiological phenomenon. The HRV cycle is second order, i.e. it results from autonomic nervous system regulation of the dynamic arterial pressure wave.